Among Qinling Mountains, there is a valley that runs through the Hanzhong Basin of the Guanzhong (Central Shaanxi) Plain. The southern mouth of the valley is named Bao, while the northern of it is called Xie. It is to the southwest of Mei County, and is about 235 kilometers long. Ever since the Warring States, people chiseled rocks, put up wooden frames, built plank roads, which continued from generation to generation and new ones added, thus it got its name “Bao Chute”. Emperor Wu (r. 140-87 BC) of the Han Dynasty ordered to build 250 kilometers of plank roads, hence the prosperity of “kilometers’ plank roads lead to everywhere”. When Bao Chutes were first built, power hadn’t been invented yet, but “firm rocks cannot be chiseled by axe”, so people had to break rocks using the methods of burning fire and surging water. The procedures were as follows: The surface of rocks was burnt, and then cold water was used to surge when the temperature of the rocks got very high, so the hot rocks split due to the effect of sudden coldness. “When there were rocks in the way, hammers were used to break them through; when there were crag and cliff, holes were chiseled, crossbars put up, timber covered, pincers and nails used to get them through; when there were dangerous ditches and gullies, stone fences were used”. Pavilions were mostly built on cliffs with 30 square centimeters in area, and a hole of 50 centimeters deep, inside which wooden and stone pillars were inserted, and were divided into higher, middle and lower rows. Planks were laid on the upper ones to form roads, while wood was set up on the lower ones as girders. Seen from distance, they were like pavilions suspended in the air. Some of them only had girders and did not have pillars, forming “thousands of girders and no pillars” as was recorded in Shui Jing Zhu (Commentary on the Waterways Classic). These were mainly used in dangerous places where it was difficult to build. In addition, there were bridges built under water. Stone pillars were laid under water. The end of pillars was firmly inserted into pre-chiseled stone holes, the upper of which was laid with beams and then covered with planks, thus “bridge of beams and pillars”. This kind of structure is still adopted by people who live along Bao Chute. The wood used in building Bao Chute is taken from what is available along the road, so it saves a lot of human and financial resources in the course of building the chutes. Ancient Bao Chute began in Bao County, Hanzhong, northward to Qin Mountains, up to the Bao River, through Maodao, Wuguan, into Jiangkou Town, Ba County, and then along the Hongya River into Wangleng, Baiyun, across Taibai County eastward, and ends at the source of Wuli slopes.
It is a manmade tunnel hole chiseled in the south mouth of Bao Chute. It is about 16.3 meters long, 4.2 meters wide, and 3.45 meters high. It was submerged in reservoir when the Stone Gate Reservoir was being built in 1970. According to the Eulogy of Stone Gate, the gate was chiseled in 1 AD during the Han Dynasty. Hence, some foreign expert once said, “The earliest manmade tunnel through mountains is in Bao City, Shaanxi”. What he meant is the mentioned stone gate.
Since Qin and Han Dynasties, the Stone Gate was opened and closed every now and then, was repaired many times, and most of the time left rubbed cliff stone sculptures. There are stone sculptures on east and west walls inside the stone gate hole, on rocks of steep slopes, escarpments, the Bao River and sand beach miles northward and southward outside the hole. Most of these sculptures were engraved during Han and Song Dynasties. Some of them are records of building and opening to traffic the Bao Chute, Stone Gate and various projects on mountains and in rivers. Some are notes of reminiscence of tours and visits. Some people estimated in the Qing Dynasty, there were over forty types of stone sculptures, among which the “thirteen articles of stone sculptures in Han and Wei Dynasties” won great reputation in Tang and Song Dynasties, and was well-known throughout the whole country. The so-called “thirteen articles of stone sculptures in Han and Wei Dynasties” were represented by the Eulogy of the Stone Gate engraved in the Eastern Han Dynasty and the Inscriptions of the Stone Gate in the Northern Wei Dynasty, both of which are on east and west walls inside the stone gate hole. The Eulogy of the Stone Gate has long been famous all over the country, and has been rare treasures in studies of the history of traffic, calligraphy and art in Ancient China, especially its calligraphy, which is the masterpiece of Hanli (an ancient style of calligraphy current in the Han Dynasty).